Method of preparing metal surfaces to receive permanent coatings



Patented July 14, 19311 TNT OFFICE i RALPH Z. HOPKINS AND ALBERT E. FELLERS, OF DETROIT, AND OSCAR T. COFFELT, OF GROS SE POINTE, .MICHIGAN, ASSIGNOBS TO HUDSON MOTOR CAR COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OF PREPARING METAL SURFACES TO RECEIVE PERMANENT COATINGS No Drawing.

and protection during manufacture of metal surfaces which are to receive a permanent protective coating, such as paint, enamel, lacquer or such materials as might be applied for protection or decorative purposes.

In the manufacture of automotive parts from sheet metal such as body panels, fenders and the like great care must be exercised to keep the metal free from rust and scale. Such articles are usually mechanically worked between dies to shape them to the desired finished form. In order to facilitate the mechanical working operation, it is customary to employ a lubricant such as mineral oil, upon the dies and to coat the shaped metal with oil to protect the surfaces while awaiting subsequent finishing operations. In order to prepare the surfaces of the shaped articles to receive a permanent .protective coating of paint, enamel, lacquer or the like,

the mineral oil must be removed. This oil' is usually burned off by subjecting the articles to a temperature of about 800 to 850 F. The removal of the oil in thismanner tends to produce a slight oxidation of the metal forming a scale which prevents the proper adhesion of the permanent protective coating. The presence of any residue of mineral oil, scale or other similar foreign materials weakens the bond between the paint or other ermanent protective coating with the result that it peels off or cracks. In the past one common practice has been as follows:

The scale upon the surface of the articles is removed by immersing the articles in an acid pickling bath for a suitable length of time after which the excess acid is removed by rinsing with water. The articles were then sometimes immersed in a solution of' weak lime water. This practice has been unsatisfactory in the manufacture of such articles as automobile fenders and the like which I must be handled considerably by workmen inasmuch as the handling tends to set up a condition upon the surface of the -metal {which produces the formation of rust. It has been found that such articles will rust while awaiting subsequent finishing operations.

It is an object of the present invention to Application filed December 29, 1928. Serial No. 329,307.

provide a method of preparing metal surfaces which will overcome these difliculties and effectively protect the surface of the metal between manufacturing operations and assure the proper adhesion of the permanent protective coating.

In carrying out the present invention any mineral oil upon the surface of the metal which has been subjected to a mechanical shaping operation may be burned off or washed off in the usual manner and the articles are then immersed or sprayed in a suitable acid pickling bath which may contain about 5 to :20 per cent. of sulphuric or other suitable acid, such as phosphoric or hydrochloric acids or the like. The excess acid is then removed from the surface of the metal by rinsing. In order to prevent acid stains upon the metal it is sometimes preferable to use as a rinsing liquid a water solution containing about one percent. of acid. During this operation the metal should not become dry; The surface isthen treated with a soap solution containing a neutralizing agent for the acid residue and a saponified oil adapted to combine with the permanent coating to be subsequently applied to the surface of the articles. Such a solution may be one containing .01 per cent. to 45 per cent. of a soluble soap Whose base is linseed oil or some 0 her oil which will combine with the enamel or paint primer. Thereafter the articles, preferably, are washed with. volatile liquids. such as are used for paint and lacquer thinners, and then dried.

It has been found that when metal surfaces are prepared in this manner that the articles have substantially no tendency to rust over long periods of time even when subjected to the conditions arising by the handling of workmen. This is probably due to the presence upon the surface of the metal of a temporary protective film. Furthermore, any foreign substances, such as iron salts, which would be detrimental to the adhesion of the permanent coating are effectively removed.

It has been found that suitable compounds may be formed by adding sodium or potassium or ammonium hydroxide or a mixture thereof to a substance containing fatty acids,

such as linseed oil or other vegetable oils, whereby the oils or other materials are saponified. It will be understood that the invention is not limited to the particular ma terials or strength of solutions mentioned. Best results have been obtained,-.however, by the use of a potassium linseed oil soap commonly called linseed oil soft soap. The soap bath should not test acid when litmus is used as an indicator.

In some cases it has been customary to place onthe sheet a protective coating which consists of wool fat or woolgrease in a volatile solvent, which evaporates and leaves a hard coating on the sheet. It will beunderstood that in this case it is desirable to remove this coating by applying a suitable solvent such as kerosene before treating the sheet accordingto our hereindescribed novel process.

at we claim is: 1. The method of protecting metal surfaces and preparing them for subsequent permanent coating which includes treating the surface with acid,-and then applying a solution which neutralizes the acid residue and also leaves on the sheet a substance which will combine with the permanent coating.

2. The method of preparing and protecting metal surfaces which have been mechanically worked to the desired form which comprises removing lubricant, pickling the table oil, removing the free shaped "metal in an acid bath, removing the excess acid, subjecting the metal to the action of a solution containing a substance which will neutralize any acid residue on the sheet and will combine with a permanent protective coating for the metal, and thereafter applyinga permanent coating to the surface of the metal.

3. The method of preparing and protecting metal surfaces which have been mechanically worked to the desired form which comprises removing lubricant, pickling the shaped metal in an acid bath, removing the excess acid, subjecting the metal to the action of a saponified fatty-acid, and applying a permanent coating to the surface of the metal.

4. The method of preparing and protecting metal surfaces which have been mechanically worked to the desired form which comprises removing lubricant, pickling the shaped metal in an acid bath,

removing the excess acid, subjecting the metal to the action of a solution containing a saponified vegeexcess with a volatile solvent and applying a permanent coating to the surface of the metal.

5. The method of preparing and protecting metal surfaces which have been mechanically worked to the desired form-which compnses removing lubricant, pickling the shaped metal in an acid bath, removing the excess'acid, subjecting the metal to the action of a solution containing soap, and applying a permanent coating to the surface of the metal.

6. In the method of preparing and protect-ing metal surfaces, the steps which comprise pickling the metal in an acid bath, re-

moving excess acid, and subjecting the metal to the action of a solution containing a substance which will combine with a permanent protective coating to be applied subsequent- .ly to the metal.

tures.

RALPH Z. HOPKINS. OSCAR T. COFFELT. ALBERT E. FELLERS. 

